This two phase project is designed to provide for the scientific training of the Investigator and to achieve a better understanding of hematopoietic stem/progenitor cell (HSPC) gene regulation through the study of the factors regulating CD34. CD34 is expressed specifically on HSPCs and is downregulated as blood cells mature. To date, it is the only well defined marker for human HSPCs. CD34+ cells can reconstitute normal hematopoiesis of all cell lineages and may be the cells of origin in a variety of leukemias. In addition, HSPCs are ideal potential targets for gene therapy. Previous studies have defined control elements which properly regulate CD34 expression in cell lines. However, these elements have yet to be studied in models of normal stem/progenitor cell hematopoiesis. Phase I will provide for the development of basic scientific knowledge and laboratory research skills through a program consisting of didactic training and active laboratory research. The goal of Phase I research will be to demonstrate that the regulatory elements which control CD34 expression in cell lines also regulate its expression in normal hematopoietic cells. Expression studies using CD34 promoter/enhancer constructs will be performed in both transgenic mouse and human CD34+ cell culture models of normal hematopoiesis. Phase II will promote Investigator independence through the conceptualization and execution of an intensive research plan based on Phase I results. The specific aims will be to isolate the minimal CD34 regulatory elements which will direct expression of a heterologous gene in HSPCs and to isolate and characterize the elements involved in the downregulation of CD34 during hematopoietic differentiation. Constructs containing these elements will be engineered and tested in our model systems. These studies should lead to a better understanding of HSPC gene regulation and lead to new insights into leukemogenesis and gene therapy.